A lamp used as a light source corresponding to a core of a lighting industry is generally formed in a tubular form, and except for special cases, includes much mercury (Hg) in a tube of the lamp. Similarly, a lamp for ultraviolet (UV) light use and a general lamp for visible light use generally include a structure of a tubular form and Hg.
A planar lamp of a planar light source form, in general, may be more conveniently and practically utilized than a tubular lamp. A plurality of optical parts and a complex structure are required for configuring the planar lamp to emit uniform light using a tubular lamp. However, since the tubular lamp is used as is, Hg is included as is even in the case of the planar light source. Also, there is a disadvantage that a total volume is increased and brightness is uneven.
Also, research on eco-friendly Hg-free lamp development excluding Hg is actively underway in the lighting industry according to the Restriction of Hazardous Substances (RoHS) directive. Also, research on the planar lamp, having many advantages in a practical aspect, is actively underway.
A photolithography is a method of forming an electrode pattern and the like on a substrate or an exposed object when manufacturing the substrate or the exposed object, and is also used in various industry fields such as a flat panel display (FPD) industry manufacturing plasma display panels (PDPs), liquid crystal displays (LCDs), and the like, a printed circuit board (PCB) industry, a semiconductor industry, a micro-electro-mechanical system (MEMS) industry, and the like.
Generally, a photolithography process includes a substrate cleaning process, a surface treatment process, a photoresist (PR) coating process, an alignment/exposure process, and a development process. In particular, an apparatus for performing the alignment/exposure process is referred to as an exposure apparatus.
The exposure apparatus is used for realizing a minute circuit pattern on the substrate, and an exposure technology is rapidly improved by improving component technologies related to exposure apparatus components, that is, a light source, an illumination system, a pattern mask, a reticle, a stage, a PR, and the like.
As semiconductor apparatuses increasingly become highly-integrated in the semiconductor industry, a high resolution is required for a circuit pattern image realizing a minute line width on a wafer in the exposure apparatus, and research on several components installed in the exposure apparatus is actively underway in order to accurately realize the minute line width in a circuit.
FIG. 1 illustrates an exposure apparatus generally used according to a conventional art. A conventional exposure apparatus generally includes a lighting system for emitting and irradiating light, an optical system for standardizing and aligning the irradiated light and controlling focus, a pattern mask including a pattern, and a substrate.
The lighting system includes a light source 130 emitting light such as a super high-voltage Hg lamp, a halogen lamp, and the like, and an oval mirror 140 condensing light of the light source 130 and irradiating light to one direction. The optical system includes a cold mirror 150, an integrator lens 170, a collimate mirror 160, and a spherical mirror 180 in order to control a direction and a feature of the light.
The light emitted from the light source 130 is condensed by the oval mirror 140 and is incident on the cold mirror 150. In this instance, a multi-layered coating processing has been performed on surfaces of the oval mirror 140 and the cold mirror 150. Accordingly, a specific UV light wavelength is reflected and other wavelengths are passed. In particular, the cold mirror 150 is a mirror reflecting light in a UV light wavelength range from the light reflected from the oval mirror 140, and allowing light of a visible light wavelength range and an infrared light wavelength range to penetrate through. Also, since the exposure apparatus used for the general exposure process uses light of a UV light range, the cold mirror 150 may be a cold mirror for UV light.
The direction of travel of the light incident on the cold mirror 150 is changed, and the light incident on the cold mirror 150 is incident on the integrator lens 170. The integrator lens 170 includes a multiple lens-array including a combination of small, independent spherical lenses. The integrator lens 170 includes a first lens 170a and a second lens 170b, and the light incident on the independent spherical lens of the first lens 170a is emitted after passing through the unit sphere lens of the second lens 170b in which optical axes are accorded again.
The light passing through the integrator lens 170 remains parallel, is reflected by the collimate mirror 160, and is incident on the spherical mirror 180. The light reflected by the spherical mirror 180 travels parallel with an optical axis, passes through a pattern mask 120, and exposes the pattern formed in the pattern mask 120 to an exposed object 100.
Currently, a number cutting methods applied for improving productivity of a pattern-forming process of the substrate or the exposed object are attempted, and expansion of an exposure area is essential for the application of the number cutting methods. However, when the exposure area is expanded by using the optical system in the conventional exposure apparatus, the effective intensity of a illuminating light is reduced. Accordingly, exposure efficiency is reduced along with pattern quality, exposure time for forming the pattern is increased, and the like.
Also, since the optical system, standardizing and aligning the light emitted from the light source, and controlling the focus, is made of a complex mirror structures and lenses, the conventional exposure apparatus creates high equipment manufacturing costs and an enormous and bulky exposure apparatus in size.
Also, as a device patterned on the exposed object 100 or a feature size becomes increasingly smaller, technical problems are generated. Specifically, in order to realize a small semiconductor device or feature size, electromagnetic radiation having a short wavelength is required to be used in order to project a pattern of a reticle or a pattern mask on the exposed object, and there are limits to the optical system having the resolution and an imaging capability required for an extreme UV light wavelength.
Also, the conventional exposure apparatus has an uneconomical aspect of high maintenance costs due to a high power consumption caused by a high voltage and a high current, and since the light source emitting light, such as a superhigh-voltage Hg lamp, a halogen lamp, and the like, has a long setup time, a low productivity yield may be a result.